Afocal relay lens system

ABSTRACT

A relay lens system designed as an afocal lens system having a magnification level of 1x and comprising a first lens group having negative refractive power, a second lens group having positive refractive power and a third lens group having negative refractive power, said relay lens system being arranged between an objective lens and an eyepiece, and used for relaying an image of an object formed by said objective lens.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an afocal relay lens system for use with microscoper.

2. Description of the Prior Art

A microscope generally has such a construction as shown in FIG. 1 and is equipped on the side of the microscopist with an objective lens O which is not used for microscopy and which is a hindrant for observation. In order to correct this defect, it is necessary to construct the microscope as shown in FIG. 2. In order to design a microscope having such a construction as shown in FIG. 2, it is necessary to arrange a relay lens system between the objective lens and an eyepiece so that an image of an object formed by the objective lens is formed again at a predetermined position. Further, in a microscope system equipped with various accessories, a relay lens system is also required for changing the imaging position of the objective lens when the accessories are to be used for microscopy. There has conventionally been known a relay lens system comprising a concave lens group and a convex lens group for shifting the image position of the objective lens in microscopes as described above. When the imaging point of the microscope without using the relay lens system is represented by O₁, the imaging point of the microscope using the relay lens system is designated by O₂ ' and the image of O₁ formed by the concave lens group L₁ is denoted by O₁ ' in a relay lens system consisting of the two concave and convex lens groups L₁ and L₂ as shown in FIG. 3, the image is shifted rearward for a distance of ε.

When A₁ O₁ is represented by α, A₁ O₁, is designated by α', A₁ A₂ is denoted by d, and focal lengths of the lens groups L₁ and L₂ are represented by f₁ and f₂ respectively in this figure, the following relations (1), (2) and (3) established by the imaging formula: ##EQU1## From these formulae (1) (2) and (3), f₁ and f₂ can be determined as follows: ##EQU2## Since the actual visual field of such a relay lens system is narrowed if it is of a magnifying type, or the image magnified by the objective lens is reduced if it is of a reducing type, both the types are undesirable. Further, a relay lens system designed for an fractional magnification level is undesirable since it results in an fractional magnification level of the entire microscope. Therefore, a relay lens system should preferably have a magnification level of 1x. When β is set at 1 in the formulae (4) and (5) above, f₁ and f₂ are calculated by the following formulae (4') and (5') respectively: ##EQU3##

FIG. 4 illustrates shift of position Q of the exit pupil of the objective by a relay lens system consisting of the concave lens group L₁ and convex lens group L₂. In this figure, the reference symbol Q' represents an image of the entrance pupil Q formed by the lens group L₁, the reference symbol Q" designates an image of Q' formed by the lens group L₂, and the reference symbols Z₁, Z₁ ', Z₂ and Z₂ ' denote positions of Q, Q' and Q" as illustrated.

Examples of numerical data for relay lens systems consisting of such concave lens group L₁ and convex lens group L₂ will be described below:

(Example 1)

In case of ε=20, d=10, β=1x and α=140:

From the formula (4'), f₁ =-140×10/20=-70

From the formula (5'), f₂ =10×(140+20 -10)/20=75

In addition, when position Z₁ of the entrance pupil is set at -35, positions Z₁ ' and Z₂ ' of Q' and Q" are calculated as follows:

From -1/Z₁ +1/Z₁ '=1/f, 1/35 +1/Z₁ '=-1/70

Hence, 1/Z₁ '=-3/70 and ##EQU4## From -1/Z₂ +1/Z₂ '=1/f₂, -1/33 +1/Z₂ '=1/75 Therefore we obtain:

Z₂ '÷-59 and

OTL (optical tube length)=(α+ε-d)-Z₂ '=209

Magnification level β_(Q) of the pupil is: ##EQU5##

(EXAMPLE 2)

In case of ε=20, d=20, β=1x and α=140:

f₁ =-140

f₂ =140

Numerical data for pupil:

Z₁ '=-28, Z₂ =48, Z₂ '=-73

OTL=213

β_(Q) =1.23

(Example 3)

In case of ε=40, d=20, β=1x and α=140:

f₁ =-70

f₂ =90

Numerical data for pupil:

Z₁ '=-23, Z₂ =43, Z₂ '=-82.3

OTL=242.3, β_(Q) =1.26

In all the examples described above, all the magnification levels β_(Q) of the pupil are larger than 1, clarifying that the pupil is magnified by the relay lens system and that position of the pupil is made farther from the eyepiece side. The pencil therefore has a larger diameter to constitute a cause for eclipse and flare. In order to prevent the eclipse, it is obliged to design the optical system on the rear side of the relay lens system so as to have a larger diameter.

Further, it will be understood, by comparing the Example 1, 2 and 3 with one another, that a larger value of ε or d will increase the value of β_(Q). (Magnification level of the pupil in the Example 2 is higher than that in the Example 1, and that in the Example 3 is higher than that in the Example 2). That is to say, the pupil is enlarged as ε and d have larger values respectively. Furthermore, the distance as measured from the image formed by the relay system to the image of the exit pupil of the objective formed by said relay lens system is prolonged as ε and d have larger values.

In order to prevent the pupil from being located at such a position, a relay lens system should desirably be of an afocal type. An afocal type of relay lens system can provide an effect which is equivalent to optical tube length remaining fixed. In other words, an afocal type of relay lens system gives no influence at all on the optical system arranged on the rear side of the relay lens system, with magnification level excepted from consideration.

In view of the foregoing, a relay lens system should preferably be of an afocal type having a magnification level of β=1. As is understood from FIG. 5, however, it is impossible to obtain an afocal type of relay lens system consisting of two concave and convex lens groups and designed for a magnification level of 1x. Conversely, an afocal type of relay lens system cannot be designed when magnification level is selected at β=1.

It is therefore impossible to obtain a desirable relay lens system which is designed as an lens system consisting of a concave lens group and a convex lens group.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide a relay lens system used for relaying an image of an object formed by an objective lens and designed as an afocal lens system having a magnification level of 1x and comprising a first lens group, a second lens group and a third lens group.

Another object of the present invention is to provide a relay lens system designed as an afocal lens system having a magnification level of 1x and comprising a first lens group having negative refractive power, a second lens group having positive refractive power and a third lens group having negative refractive power.

A further object of the present invention is to provide a relay lens system comprising a first lens group, a second lens group and a third lens group and so designed as to satisfy the following conditions: ##EQU6## wherein the reference symbols f₁, f₂ and f₃ represent focal lengths of said lens groups respectively, the reference symbols s₀ designates the distance in millimeters as measured from the rear focal point of said first lens group to said second lens group, the reference symbol ε denotes displacement of image carried out by said relay lens system and the reference symbol d represents the distance between said first lens group to said third lens group.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation illustrating construction of the miscroscope which has conventionally been used;

FIG. 2 shows a schematic representation illustrating an application mode of a relay lens system;

FIG. 3 shows a diagram illustrating positional relationship in the optical system of the conventional relay lens system;

FIG. 4 shows a diagram illustrating position of the pupil in the conventional relay lens system;

FIG. 5 shows a diagram illustrating an afocal lens system consisting of a concave lens group and a convex lens group;

FIG. 6 shows a sectional view illustrating composition of the optical system in the relay lens system according to the present invention;

FIG. 7 shows a diagram illustrating position of the pupil in the relay lens system according to the present invention;

FIG. 8 shows a sectional view illustrating composition of a relay lens system preferred as an embodiment of the present invention; and

FIG. 9 shows curves illustrating the aberration characteristics of the embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In relay lens system consisting of a first lens group L₁, a second lens group L₂ and a third lens group L₃ as shown in FIG. 6, there is established the following relations (6) through (12): ##EQU7## (7) f₁ +s₀ +s₀ '+f₃ =d ##EQU8## (9) ε=x₁ +2f₁ +s₀ '+2f₃ +x₂ ' ##EQU9## wherein the reference symbol x₁ represents distance 0₁ F₁, the reference symbol x₁ ' designates distance F₁ 'O₁ ', the reference symbol s₂ ' denotes distance O₂ 'A₂, the reference symbol s₀ represents distance F₁ 'A₂, the reference symbol s₀ ' designates distance A₂ F₃, and the reference symbols f₁, f₂ and f₃ denote focal lengths of the lens groups L₁, L₂ and L₃ respectively.

Among the relations mentioned above, the formula (6) is a condition established based on the fact that the relay lens system is of an afocal type designed for a magnification level of 1x, and the formulae (7) through (12) are determined by applying the formulae for lens systems. From these formulae (6) through (12), focal lengths f₁, f₂ and f₃ of the respective lens groups are calculated as follows: ##EQU10## Signs and values of the respective focal lengths f₁, f₂ and f₃ are dependents on selection of ε, d and s₀. However, it is necessary to design so as not to make ε nearly equal to d since f₁ and f₂ will have very small values when ε is nearly equal to d. Since ε has actually a given value, the value of d is substantially determined. Therefore, focal length of each lens group is substantially dependent on value of s₀. From a viewpoint of correcting aberrations, it is preferable to select a values of s₀ within a range defined by the following condition:

25<s₀ <55

That is to say, when s₀ has a value smaller than 25, |f₁ | and |f₂ | will have two small values, thereby making it difficult to correct aberrations by the lens groups L₁ and L₂. If s₀ is larger than 55, in contrast, |f₃ | will have a very small value, thereby making it difficult to correct aberrations by the lens group L₃.

The pupil Q is located at the position shown in FIG. 7. In this figure, Q' represents an image of Q, Q" designates an image of Q' and Q"' denotes an image of Q". Therefore the pupil Q is shifted to Q"' by the relay lens system.

Now, an example of numerical data for a relay lens system designed as an afocal lens system having a magnification level of 1x will be described below:

In case where ε is selected at 20 and d is set at 40,

the formula (13) gives f₁ =-1/2s₀, and

the formula (15) gives f₃ =-1/2s₀ ##EQU11## When s₀ is set at 20, 30, 40, 50 and 60, f₁, f₂ and f₃ have the values listed below:

    ______________________________________                                         s.sub.0 = 20                                                                              s.sub.0 = 30                                                                            s.sub.0 = 40                                                                             s.sub.0 = 50                                                                          s.sub.0 = 60                              ______________________________________                                         f.sub.1                                                                             -10       -15      -20     -25    -30                                     f.sub.2                                                                              15       18.75     20     18.75   15                                     f.sub.3                                                                             -30       -25      -20     -15    -10                                     ______________________________________                                    

Among the numerical data listed in the above table, let us take s₀ =40 as an example. That is to say, in a case of ε=20, d=40, s₀ =40, s₁ =140 and Z₁ =-35, position of image and position of the pupil are calculated as follows:

Position of image: ##EQU12## Position of the pupil: ##EQU13## As is understood from the foregoing descriptions and calculation example, it is possible to design a relay lens system having a magnification level of 1x as an afocal lens system consisting of three lens groups. This lens system is preferable as a relay lens system since the distance as measured from the image of an object formed by the relay lens system to the image of the pupil of the objective lens formed by the relay lens system is equivalent to the distance from the image of the object formed by the objective lens to the pupil of the objective lens.

FIG. 8 shows composition of a relay lens system preferred as an embodiment of the present invention comprising a first lens group L₁ consisting of a negative cemented doublet component, a second lens group L₂ consisting of a positive cemented doublet component and a positive lens component, and a third lens groups L₃ consisting of a negative lens component. The relay lens system has the following numerical data:

    ______________________________________                                         r.sub.1 =                                                                               -31.329                                                                        d.sub.1 = 1.5                                                                             n.sub.1 = 1.6425                                                                            ν.sub.1 = 58.37                            r.sub.2 =                                                                               16.617                                                                         d.sub.2 = 3.0                                                                             n.sub.2 = 1.497                                                                             ν.sub.2 = 81.60                            r.sub.3 =                                                                               240.41                                                                         d.sub.3 = 10.0                                                        r.sub.4 =                                                                               695.54                                                                         d.sub.4 = 2.0                                                                             n.sub.3 = 1.56138                                                                           ν.sub.3 = 45.18                            r.sub.5 =                                                                               48.835                                                                         d.sub.5 = 6.0                                                                             n.sub.4 = 1.48749                                                                           ν.sub.4 = 70.15                            r.sub.6 =                                                                               -27.401                                                                        d.sub.6 = 0.5                                                         r.sub.7 =                                                                               25.499                                                                         d.sub.7 = 6.5                                                                             n.sub.5 = 1.5119                                                                            ν.sub.5 = 58.14                            r.sub.8 =                                                                               -53.219                                                                        d.sub.8 = 10.5                                                        r.sub.9 =                                                                               -24.213                                                                        d.sub.9 = 2.5                                                                             n.sub.6 = 1.56013                                                                           ν.sub.6 = 46.99                            r.sub.10 =                                                                              33.222                                                                         d.sub.0 = 9,                                                                                l = 60,     ε = 20                               Magnifica-         Magnifi-                                                    tion of image 0.998 × ,                                                                     cation of pupil 1.001 ×                               f.sub.1 = -31.6,                                                                              f.sub.2 = 22.2,                                                                           f.sub.3 = -24.6                                      ______________________________________                                    

Curves illustrating the aberration characteristics of the above-mentioned embodiment are illustrated in FIG. 9.

As an ideal relay lens system, an afocal lens system designed for a magnification level of 1x has been described above. However, it is possible to design a relay lens system for β=1 and β_(Q) ≠1 by deviating magnification level of the pupil within such a range as to constitute no hindrance to use of optical system arranged on the rear side of the relay lens system. Such a means will facilitate lens design by increasing flexibility for lens design and especially be advantageous for correcting aberrations in relay lens systems. 

I claim:
 1. In a relay lens system arranged between an objective lens and an eyepiece and used for relaying an image of an object formed by said objective lens, a relay lens system is designed as an afocal lens system having a magnification level of 1X and comprises a first lens group, a second lens group and a third lens group, wherein said first lens group is a negative lens group, said second lens group is a positive lens group and said third lens group is a negative lens group, and wherein said relay lens system is located between the objective and the image position of the objective.
 2. A relay lens system according to claim 1 satisfying the following relations: ##EQU14## wherein the reference symbols f₁, f₂ and f₃ represent focal lengths of said first, second and third lens groups respectively, the reference symbols s₀ designate the distance in millimeters as measured from the rear focal point of said first lens group to said second lens group, the reference symbol ε denote displacement of image caused by said relay lens system and the reference symbol d represents distance between said first lens group and said third lens group.
 3. A relay lens system according to claim 2 wherein said first lens group consists of a negative cemented doublet component, said second lens group consists of a positive cemented doublet component and a positive lens component, and said third lens group consists of a negative lens component, said relay lens system having the following numerical data:

    ______________________________________                                         r.sub.1 =                                                                               -31.329                                                                        d.sub.1 = 1.5                                                                             n.sub.1 = 1.6425                                                                            ν.sub.1 = 58.37                            r.sub.2 =                                                                               16.617                                                                         d.sub.2 = 3.0                                                                             n.sub.2 = 1.497                                                                             ν.sub.2 = 81.60                            r.sub.3 =                                                                               240.41                                                                         d.sub.3 = 10.0                                                        r.sub.4 =                                                                               695.54                                                                         d.sub.4 = 2.0                                                                             n.sub.3 = 1.56138                                                                           ν.sub.3 = 45.18                            r.sub.5 =                                                                               48.835                                                                         d.sub.5 = 6.0                                                                             n.sub.4 = 1.48749                                                                           ν.sub.4 = 70.15                            r.sub.6 =                                                                               -27.401                                                                        d.sub.6 = 0.5                                                         r.sub.7 =                                                                               25.499                                                                         d.sub.7 = 6.5                                                                             n.sub.5 = 1.5119                                                                            ν.sub.5 = 58.14                            r.sub.8 =                                                                               -53.219                                                                        d.sub.8 = 10.5                                                        r.sub.9 =                                                                               -24.213                                                                        d.sub.9 = 2.5                                                                             n.sub.6 = 1.56013                                                                           ν.sub.6 = 46.99                            r.sub.10 =                                                                              33.222                                                                         d.sub.0 = 9,                                                                                l = 60,     ε = 20                               Magnifica-         Magnifi-                                                    tion of image 0.998 × ,                                                                     cation of pupil 1.001 ×                               f.sub.1 = -31.6,                                                                              f.sub.2 = 22.2,                                                                           f.sub.3 = -24.6                                      ______________________________________                                    

wherein the reference symbols r₁ through r₁₀ represent radii of curvature on the surfaces of the respective lens elements, the reference symbols d₁ through d₈ designate thicknesses of the respective lens elements and airspaces reserved therebetween, the reference symbols n₁ through n₆ denote refractive indices of the respective lens elements, the reference symbols ν₁ through ν₆ represent Abbe's numbers of the respective lens elements, the reference symbol d₀ designates distance as measured from the contact surface of the objective lens to said first lens group and the reference symbol l denotes distance as measured from the contact surface of the objective lens to the attached surface of the relay lens system. 